Modern private branch exchanges (PBX) use a computer to control a switching network. PBXs are also referred to as customer switching systems or private automatic branch exchanges (PABX). In addition to controlling the PBX, the computer is continuously running basic diagnostic tests not only on itself but also on the switching network and communication facilities interconnecting the PBX to other PBXs and other types of computer systems. In addition to permanent faults/alarms, these diagnostic tests find many transitory faults within the PBX. The transitory faults may indicate that a component of the PBX is marginally faulty or that the PBX's environmental conditions have induced a failure in the PBX. Such environmental conditions result from a variety of sources ranging from error conditions on the communication facilities to electrical noise in the AC power supplied to the PBX at its site. Each fault occurring on a PBX must be investigated by a service technician to determine the severity of the fault. When a PBX manufacturer has thousands of PBXs to maintain in the field, the cost of making such investigations becomes enormous.
Some manufacturers have equipped their PBXs to report all faults to a centralized service reporting center. A technician at the service reporting center reviews the faults reports and then remotely accesses the PBX to determine the cause of the faults. Whereas the ability of a technician to remotely maintain PBXs is an improvement, the manufacturer still incurs considerable costs in maintaining PBXs in the field because of the labor cost of technicians.
Expert systems have been extensively used to assist in the maintenance of remote systems by directly supporting maintenance technicians. U.S. Pat. No. 4,697,243 discloses an expert system which assists technicians in the maintenance of elevators. In that system, an expert system running on a central computer leads an on-site technician through a diagnostic session with menus, questions, and directions displayed to the technician on a remote terminal. The technician communicates fault and test data to the expert system via the terminal. The expert system then diagnoses the elevator fault and sends the diagnosis back to the technician who then repairs the elevator.
U.S. Pat. No. 4,517,468 discloses an expert system executing on a central computer for collecting data from remote steam turbine generator power plants. After collecting the data from a plant, the expert system determines if a fault condition exists in that plant by using field knowledge incorporated into the expert system. Upon detection of a fault condition, the expert system communicates the information to the plant operator with suggested actions to be taken. However, the expert system does not directly run any tests on the plant or alter the state of data within the plant. Further, the system requires an unique mechanism for accessing the data from the plant since the system cannot use the same means to gather data as used by technicians.
The problem with prior expert systems that diagnose fault conditions in remote computer systems, is that they require a human technician to determine the fault condition or to test and retire fault alarms in those systems. Also those expert systems require special mechanisms for gaining access to remote system data which add to the operating costs.